Problem: Simplify the following expression: $z = \dfrac{r}{10} \div \dfrac{8r}{7}$
Answer: Dividing by an expression is the same as multiplying by its inverse. $z = \dfrac{r}{10} \times \dfrac{7}{8r}$ When multiplying fractions, we multiply the numerators and the denominators. $z = \dfrac{ r \times 7 } { 10 \times 8r}$ $z = \dfrac{7r}{80r}$ Simplify: $z = \dfrac{7}{80}$